/Engine/Source/Runtime/SlateCore/Public/FastUpdate/SlateInvalidationRoot.h
the cached draw elements for this window and its widget hierarchy
[FSlateInvalidationResult](API\Runtime\SlateCore\FastUpdate\FSlateInvalidationResult) PaintInvalidationRoot ( const [FSlateInvalidationContext](API\Runtime\SlateCore\FastUpdate\FSlateInvalidationContext) & Context )